This nonprovisional application claims priority under 35 U.S.C. xc2xa7 119(a) Patent Application No. 2002-0035513 filed in KOREA on Jun. 25, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a color cathode-ray tube, and more particularly to a cathode-ray tube employing a tint or dark tint glass panel in which an optimal transmittance is achieved by solving a problem of deterioration of a brightness balance of the periphery of the screen and the center of the screen caused by the difference between the transmittances in the center and periphery of the screen.
2. Background of the Related Art
FIG. 1 illustrates a configuration of a related art flat color cathode-ray tube.
Referring to FIG. 1, the related flat color cathode-ray tube forms a vacuum tube by which a front side glass panel 1 is combined with a rear side glass funnel 2 and sealed up, and therefore its interior is maintained in a vacuum state.
A fluorescent screen 4 is formed on the internal surface of the panel 1. An electron gun assembly 13 is installed in a neck of the funnel 2 facing the fluorescent screen 4.
A shadow mask 7 that performs a color selection is installed between the fluorescent screen 4 and the electron gun assembly 13 at a predetermined distance from the fluorescent screen 4. The shadow mask 7 is fitted to a mask frame 3 and upheld elastically by a spring 8 in order to be supported by the panel 1 with a stud pin 12.
The mask frame 3 is coupled to an inner shield 9 made of magnetic materials to reduce an effect of the terrestrial magnetic field in the rear portion of the cathode-ray tube for reducing the movements of electron beams caused by an external magnetic field.
A Convergence Purity Magnet (CPM) 10 for adjusting red (R), green (G), blue (B) electron beams is installed in the neck of the funnel 2 in order to converge the electron beams 6 into a single point, and a deflection yoke 5 is also placed for deflecting the electron beams.
In addition, a reinforcement band 11 is installed to reinforce the front side glass according to the internal vacuum state.
The operation of the above-described flat color cathode-ray tube is illustrated hereinafter. The electron beams 6 emitted from the electron gun assembly 13 are deflected in vertical and horizontal directions by the deflection yoke. The deflected beams pass through beam through-holes of the shadow mask 7 and land on the front side of the fluorescent screen 4, thereby displaying a desired color image.
Here, the CPM 10 adjusts the convergence and purity of the R, G, B electron beams 6. The inner shield 9 blocks the effect of the terrestrial magnetic field from the rear side of the cathode-ray tube.
FIG. 2 illustrates the structure of the shadow mask.
Referring to FIGS. 1 and 2, the shadow mask 7 is placed in a dome shape while maintaining a predetermined distance from the internal surface of the panel 1.
The shadow mask 7 is comprised of an effective surface portion 31 having a plurality of slots which are dot or stripe type electron beam through-holes formed in the center, an ineffective surface portion 32 surrounding the effective surface portion 31 without the slots, and a mask skirt 33 cut and curved vertically from the ineffective surface portion 32 at the outermost portions of the skirt.
The frame 3 is welded onto the mask skirt 33.
The shadow mask 7 has a 0.1 to 0.3 mm thickness and comprises the plurality of slots 34, which are passages through which the electron beams 6 pass and, are formed in a predetermined arrangement in the effective surface portion 31. The slots 34 are arranged in a plurality of rows whose dot or stripe type holes have a predetermined pitch.
This flat color cathode-ray tube reproduces an image by deflecting the electron beams 6 that have been emitted from the electron gun assembly 13 mounted on the end of the funnel 2 in up, down, right and left directions with the deflection yoke 5 mounted on the external surface of the funnel 2. Thereafter, the deflected electron beams land on the fluorescent screen 4 formed on the internal surface of the panel 1 by passing through the shadow mask 7 having the plurality of the through-holes and functions as a color selector.
At this time, brightness and darkness of the image depend largely on a degree of illumination of the fluorescent screen 4 formed on the internal surface of the panel 1 by the electron beams 6, and an amount of the electron beams 6 passing through the slots 34 that are stripe-type holes formed in the shadow mask 7.
When the electron beams 6 pass the slots 34 (the electron beam through-holes) of the shadow mask 7, their transmittance is about 14 to 20%. The transmittance of the electron beams passing through the fluorescent screen 4 that has been spread on the internal surface of the panel 1 after passing through the shadow mask 7 is 45 to 60%.
Finally, the electron beams 6 pass the panel 1 to display the image.
In the panel 1 of the conventional color cathode-ray tube, a clear glass, the central transmittance of which is above 75% has a final central transmittance of about 54% and a peripheral transmittance of 47%.
When a tint glass or dark tint glass is employed as a panel, a contrast characteristic indicating definition becomes improved but the peripheral transmittance drops sharply, and as a result, the problem of deterioration in brightness balance of the periphery to the center occurs.
That is, the clear glass has a final central transmittance of about 54% and a peripheral transmittance of about 47%, but the tint glass has transmittances of about 54% and 35%, respectively. Thus, the peripheral transmittance is substantially lowered in a case of the tint glass when compared with the clear glass causing the central to peripheral brightness balance to be deteriorated.
To solve these problems, a method for reducing the thickness of the panel 1 to improve the transmittance of the panel 1 has been studied.
With respect to a shape of the panel 1, the external surface is almost flat and the internal surface has a kind of dome shape, the center of which is the thinnest, and the panel becomes thicker toward the periphery. Therefore, reducing the thickness means making the dome shape of the internal surface of the panel 1 flat.
If this is done, however, the shape of the shadow mask 7, the curvature of which is similar to the curvature of the dome shape of the internal surface of the panel 1 should also be flat.
As the shadow mask 7 becomes flat, its structural strength is weakened causing problems such as a howling effect.
In addition, since curvature deformation caused by small shocks or collisions occur relatively easily due to the structural weakening, a problem of generating image distortion may occur.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
The present invention is for a cathode-ray tube and has an object of solving a foregoing problem of degradation in a brightness balance of the periphery to center of a screen due to a difference between glass transmittances for a cathode-ray tube employing a tint or a dark tint glass panel.
The foregoing object and advantages are realized by providing a cathode-ray tube comprising a panel having a substantially flat external surface and an internal surface formed with a fluorescent screen in a predetermined curvature, and a shadow mask placed a predetermined distance apart from the internal surface of the panel and a plurality of electron beam through-holes are formed therein, wherein the cathode-ray tube is characterized by having a central transmittance of the panel as 40-75%, a transmittance ratio of the center to a periphery of the panel as 1.4xcx9c2.2, and the ratio of the peripheral transmittance to the central transmittance satisfying the following relationship: 0.85xe2x89xa6Tmd/Tmcxe2x89xa61.00, wherein, Tmd is the peripheral transmittance and Tmc represents the central transmittance.
A cathode-ray tube according to the present invention has advantages of improving the brightness balance and definition of the screen by raising the brightness of the periphery by improving distribution of the transmittances of the center and periphery in order to raise the ratio of the central to peripheral transmittances.
There is an additional advantage of improving contrast by employing a high definition panel such as tint or dark tint glass.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.